Question: Ashley is 9 years older than Gabriela. Sixteen years ago, Ashley was 4 times as old as Gabriela. How old is Ashley now?
Answer: We can use the given information to write down two equations that describe the ages of Ashley and Gabriela. Let Ashley's current age be $a$ and Gabriela's current age be $g$ The information in the first sentence can be expressed in the following equation: $a = g + 9$ Sixteen years ago, Ashley was $a - 16$ years old, and Gabriela was $g - 16$ years old. The information in the second sentence can be expressed in the following equation: $a - 16 = 4(g - 16)$ Now we have two independent equations, and we can solve for our two unknowns. Because we are looking for $a$ , it might be easiest to solve our first equation for $g$ and substitute it into our second equation. Solving our first equation for $g$ , we get: $g = a - 9$ . Substituting this into our second equation, we get the equation: $a - 16 = 4($ $(a - 9)$ $ -$ $ 16)$ which combines the information about $a$ from both of our original equations. Simplifying the right side of this equation, we get: $a - 16 = 4a - 100$ Solving for $a$ , we get: $3 a = 84$ $a = 28$.